Astronomy Trivia Challenge: Can You Answer These Questions About the Night Sky?

[chroot]

You got it, Marcus. Lineweaver's little 30-pager is a great overview of the state of cosmology right now, you're right! It inspired my question. I'm not sure who sent the link to me -- it was probably you. :)

Anyway, it is a shame that Astronomy magazine and others are so haphazard with their details. It's pretty much unacceptable for a magazine like Astronomy to assert in March 2003 that the size of the observable universe is 14 billion light years. Even if you ignore the recent findings about the accelerating expansion, this is patently wrong. Light travel time is just not a good way to describe distances in a universe that has changed in size.

The accelerated expansion, by the way, is the reason why the particle horizon maxes out at 62 billion light-years -- if the expansion were constant, we would eventually be able to see everything in the entire universe.

Your turn, marcus.

- Warren

 

[marcus]

Originally posted by chroot


The accelerated expansion, by the way, is the reason why the particle horizon maxes out at 62 billion light-years -- if the expansion were constant, we would eventually be able to see everything in the entire universe.

Right! And that is hard to grasp too----without accelerated expansion even objects receding at greater than c could emit light that eventually reaches us----infinity being as it were a long time The idea of being able to see everything if you wait long enough is staggering. But with accelerated expansion it is only a finite piece that we will ever get to see no matter how long we wait. Cool ideas they get to deal with, these cosmologists.

I had a question ready, which can serve here in the game and also I posted it out in the "lineweaver" thread. Answers there don't count in the game. Here it is:

-----------------

This question is based on Lineweaver's Figure 1, top section'
There are three diagrams in Figure 1, I mean the top one.

If you go to the IPAC-Caltech site then you can enlarge the diagrams to fill the screen.

http://nedwww.ipac.caltech.edu/leve...r_contents.html

It's also convenient to print it out which you can do from the Los Alamos archive site-----tho the diagrams are smaller printed out.

http://arxiv.org/abs/astro-ph/0305179

Either way, what you see in the figure is a tear-drop shaped lightcone

And also you see a curve showing the extent of the "HUBBLE SPHERE" and he explains what he means by that.

Question 1: What are meant by lightcone and Hubble sphere?

There is a point in the diagram where the Hubble sphere and lightcone intersect. The Hubble sphere line crosses the side of the teardrop shaped lightcone.

Question 2: What does the intersection signify? Why does it come at the widest point of the lightcone----where the side of the lightcone is vertical?

 

[marcus]

I just noticed the rules Nicool posted at the beginning of the thread say I should post a new question since this one wasnt answered in 3 days

Originally posted by marcus

Question 1: What are meant by lightcone and Hubble sphere?

There is a point in the diagram where the Hubble sphere and lightcone intersect. The Hubble sphere line crosses the side of the teardrop shaped lightcone.

Question 2: What does the intersection signify? Why does it come at the widest point of the lightcone----where the side of the lightcone is vertical?

Just to conclude, the Hubble radius is the current distance to where space is receding at c ( Lineweaver, caption to fig. 1).
Within the Hubble sphere space is receding at speeds < c. Outside it is receding at > c. the radius of the h. sphere changes with time as shown in the figure.

The past lightcone essentially shows the paths along which light now reaching us has traveled----in a simple 2D spacefime diagram the lightcone line is the path of a ray of light coming towards us for the whole history of the universe and reaching us today.

Where the two curves intersect is where light started out towards us in a region of space receding from us (at that time) at speed c------so for the first few days the light didnt get any closer to us! It's speed towards us was canceled by the Hubble flow away from us. So its time-line goes vertically up the diagram parallel to ours. But after a while it begins making progress "swimming upstream" against the current of the Hubble flow (another term for the expansion of space).

Below that intersection light starting out towards us is initially swept back (teardrop shape of lightcone, below its widest point)

I'll think of another and post it.

 

[marcus]

another question
background to question:
the expanding universe model of cosmology was used
in 1948 (Alpher/Herman) to predict the CMB
over 10 years later the CMB was found and it had roughly
the temperature they had predicted-----a classic longshot.
They had predicted 5 kelvin and it turned out to be 2.726.


Another background, with a different temperature, is also
predicted by the model. (Lineweaver p23 section 7.4)

This other cosmic background temp has not as yet been measured.

what is this other background and what (roughly) is its predicted temperature?

 

[subtillioN]

the 2.7k CMB is simply the ambient temp of the ubiquitous intersteller Hydrogen. This temp was actually more correctly predicted by the steady state model as I recall.

See this link:
http://www.Newtonphysics.on.ca/COSMIC/Cosmic.html

" Abstract.
It is recalled that one of the most fundamental laws of physics leads to the prediction that all matter emits electromagnetic radiation. That radiation, called Planck's radiation, covers an electromagnetic spectrum that is characterized by the absolute temperature of the emitting matter. From astronomical observations we observe that most matter in the universe is in the gas phase at 3 K. Stars of course are much hotter. The characteristic Planck's spectrum, corresponding to 3 K, is actually observed in the universe exactly as required.
However, in the standard model of the universe, the simple fundamental Planck's law has been ignored. It is claimed that the observed radiation comes from a combination of complicated hypotheses, involving an elaborate "creation mechanism" called the Big Bang. After this event, the radiation would have been emitted at a single instant when matter became decoupled from radiation. Finally, that radiation would have been shifted increasing its wavelength about 1000 times. We show that the 3 K radiation spectrum observed is simply the Planck's radiation emitted by gaseous matter at 3 K. "

 

[marcus]

Originally posted by subtillioN
the 2.7k CMB is simply the ambient temp of the ubiquitous intersteller Hydrogen. This temp was actually more correctly predicted by the steady state model as I recall.

See this link:
http://www.Newtonphysics.on.ca/COSMIC/Cosmic.html

a stable unexpanding universe in equilibrium at 3 kelvin
is a charming thought but the question was about
something predicted by the prevailing model
there is this other background that mainstream cosmology
predicts is there and that it has a certain black body temperature,
the question is about what temp is predicted by the model

BTW when they do measure the temp it will be a good test
of the standard cosmic model, right?

so what is this other background I am referring to?
and what is the predicted temp?

 

[marcus]

Originally posted by Nicool002
Hi guys! Most of you know how this works but for the newcomers:

The rules are this: someone will ask a question and if the question is not answered correctly within 3 days then a new question will be posted. If an answer to a question is posted and the person that posted the question does not respond to the answer within 2 to 3 days, then the first person to have answered the question will then be able to post their own question. HAVE FUN AND LEARN!

I will start:

Question: What is the brightest star in the Northern Sky? (excluding the sun)

This game can be a lot of fun and interesting.
Since no one has answered in 3 days I think it is up for grabs.
Anyone can ask a question
or so I think from looking at Nicool's rules

 

[marcus]

I asked the last question in the Q/A game and it has gone unanswered for more than 3 days so I will answer it myself and maybe pose another.

Originally posted by marcus
another question
background to question:
the expanding universe model of cosmology was used
in 1948 (Alpher/Herman) to predict the CMB
over 10 years later the CMB was found and it had roughly
the temperature they had predicted-----a classic longshot.
They had predicted 5 kelvin and it turned out to be 2.726.


Another background, with a different temperature, is also
predicted by the model. (Lineweaver p23 section 7.4)

This other cosmic background temp has not as yet been measured.

what is this other background and what (roughly) is its predicted temperature?

The other background (besides the microwave background) which the expanding universe model predicts is the NEUTRINO BACKGROUND and this also has a thermal distribution with a definite temperature, just like the microwave background does, but the model predicts a DIFFERENT TEMPERATURE!

The microwave temperature of space has been measured at 2.73 kelvin, corresponding to a redshift z = 1100.

The predicted neutrino background temperature is 1.9 kelvin.

The fact that the two temps differ the way they do provides for a sensitive test of the model at some time in the future when the neutrino background will have been well-enough studied to determine its temperature. I think Lineweaver's discussion of this on page 24 is pretty interesting. It explains why T_CMB should be hotter than T_neutrino by a certain amount.

 

[marcus]

A new question for the Q/A game

We know that Aristarchus of Samos (who flourished around 270 BC) maintained that the Earth travels around the sun and that the cycle of day and night is caused by the Earth's rotation.

The main reason we know about Aristarchus and his heliocentric model is because it is described in a book written a few years later by somebody else.

(Unfortunately Aristarchus original writings proposing the heliocentric model have been lost, although his calculation of the relative sizes of the earth, moon, and sun has been preserved)

What is the book which is our primary source about this and who wrote it?


For "extra credit", why did the Greek contemporaries of Aristarchus mostly reject his proposed heliocentric model?

 

[Shadow]

was it De architectura by virtruvis?

 

[marcus]

Originally posted by Shadow
was it De architectura by virtruvis?

No, the book was by Archimedes.

Archimedes described the heliocentric model (later popularized by Copernicus) around 250 BC in a book called the "Sand-Reckoner."

Copernicus knew about this and made a reference to it in one of his manuscripts, giving Aristarchus the credit for the discovery.

In "Sand-Reckoner" Archimedes describes Aristarchus model of the universe as a sphere with the sun in the middle and he calculates the number of grains of sand that would be needed to fill it.

There is an odd similarity between this and the present excitement among modern cosmologists about how much matter and energy of various sorts the universe contains.

the rules of this "Astronomy" Q/A game suggest that if a question goes unanswered for 3 days or more (which this has) then another should be provided, so I will think of one unless someone else gets to it before I do

 

[marcus]

the most distant quasar

What is the most distant object known to astronomers?
I mean a localized object----a certain quasar in fact---rather than diffuse radiation like the microwave background and ancient neutrinos.

What is its observed redshift?

 

[Shadow]

Well there is a baby galaxy that Astronomers have found and it took 122 billion years for it's light to reach Earth but that is, in fact NOT a quasar... when you say local, do you mean in this galaxy?

 

[chroot]

It's a quasar (I can find neither its name nor its location) at redshift 6.4, discovered by the Sloan DSS.

- Warren

 

[marcus]

Originally posted by chroot
It's a quasar (I can find neither its name nor its location) at redshift 6.4, discovered by the Sloan DSS.

- Warren

You're right! It is your turn

We both probably saw the announcement in Ned Wright's "news of the universe"-----the quasar was discussed by Bob Becker (of the Sloan sky survey) around November 2002 at a talk that Wright referred to

The direction to it is very close to the star in the Big Dipper called "gamma UMa"

You teach astronomy, I know, but for anybody who doesn't know which star is "gamma" in that constellation, imagine the dipper in standard dipper position and picture where the handle joins on to it: that star is delta and gamma is the one just beneath it.

like, gamma is the lower left corner star of the dipperbowl

the quasar is about a degree below that corner star
and indeed the reshift is a huge 6.4, imagine wavelengths stretched out to more than seven times original length!

Think of a good one Warren.

 

[Shadow]

Ummm...Chroot are you going to post?

 

[marcus]

Originally posted by Shadow
Ummm...Chroot are you going to post?

Shadow, do you have a question you want to post?
The rules say something like if the thread is inactive for three days then somebody should do something.

I think Nicool wrote something about this at the start.

If you have a question, why not post it?

If you don't have one you want to ask, please reply to that effect and unless chroot shows up I will think of one

Id rather you did though since its time for some new people

 

[Shadow]

Okay then.

1) What is Helioseismology and what do you do? (This may be little unclear so if you don't get it, then just tell me and I will explain what I mean)

2) What two kinds of radiation are Gamma Rays converted into by the time they emerge from the suns photosphere?

 

[LURCH]

Originally posted by Shadow
Okay then.

1) What is Helioseismology and what do you do? (This may be little unclear so if you don't get it, then just tell me and I will explain what I mean)

2) What two kinds of radiation are Gamma Rays converted into by the time they emerge from the suns photosphere?

Two off-the-cuff geusses;

1) Just judging from the composition of the word itself, I would geuss it's the study of turbulance on the Sun's surface (prob. to determine what's happeneing underneath).

2) Heat and light?

 

[Shadow]

Number 1 is close but not exactly right but I will give it to you...it isn't of the suns surface, but the suns interior.

Number two is wrong

 

[chroot]

1) The study of modes of pressure-wave oscillations in the sun's interior.

2) The gamma-rays emitted by the nuclear reactions at the Sun's core are converted to lower-energy forms of electromagnetic radiation by the non-reacting envelope. There is no 'second' form of radiation attributable to the gamma rays themselves.

- Warren

 

[Labguy]

Wouldn't it be electromagnetic and neutrino? It can't be X-ray, because that is one form of EM. And, neutrinos are produced at the same time as the gamma radiation, but aren't a "product" of the gamma radiation, like Chroot said.

 

[Shadow]

Actually (and I can understand why you don't have these...it was a question with a few possible answers) I was looking for "by the time Gamma Rays emerge ffrom the photosphere, the energy is converted in infrared and optical radiation"

 

[chroot]

Originally posted by Shadow
Actually (and I can understand why you don't have these...it was a question with a few possible answers) I was looking for "by the time Gamma Rays emerge ffrom the photosphere, the energy is converted in infrared and optical radiation"

Well, this is simply not correct, as it's also converted into ultraviolet, X-ray, radio, etc.

- Warren

 

[LURCH]

Originally posted by Shadow
Actually (and I can understand why you don't have these...it was a question with a few possible answers) I was looking for "by the time Gamma Rays emerge ffrom the photosphere, the energy is converted in infrared and optical radiation"

That's what I said; heat and light!

 

[Shadow]

Actually (and I can understand why you don't have these...it was a question with a few possible answers) I was looking for "by the time Gamma Rays emerge ffrom the photosphere, the energy is converted in infrared and optical radiation"

I clearly said right there that it was a question with a few possible answers but I was also looking for two specific answers and lurch got it right i just missed it because I was looking optical and infrared I think my eyes just skipped over heat and light. Your go LURCH

 

[LURCH]

'K,

When/where on Earth will the next total Solar eclipse be?

 

[chroot]

23 November 2003, in *gasp* Antarctica.

http://sunearth.gsfc.nasa.gov/eclipse/TSE2003/TSE2003.html

- Warren

 

[LURCH]

[>:)] (that's bull's eye) Chroot.

Think I might miss that one!

Your go.

 

[marcus]

Lurch posed a question about a solar eclipse, Chroot answered correctly, Lurch replied and said it was Chroot's turn to ask. But over 3 days have gone by and he has not posted. (People go on vacation or get busy at work etc.)

Nicool's rules cover this kind of situation in other explicit cases.

Originally posted by Nicool002
Hi guys! Most of you know how this works but for the newcomers:

The rules are this: someone will ask a question and if the question is not answered correctly within 3 days then a new question will be posted. If an answer to a question is posted and the person that posted the question does not respond to the answer within 2 to 3 days, then the first person to have answered the question will then be able to post their own question. HAVE FUN AND LEARN!

In the spirit, if not the letter, let's extend the rules of order to this case.

Lurch, you asked the last question. Why don't you give Warren one day to take his turn as asker, and if he doesn't then you take another turn and ask the next question?

Shadow, if Lurch is also on vacation, then its up for grabs. You could pose one

 

[LURCH]

That seems equitable. C'mon, Chroot, let's hear from ya!

 

[Labguy]

Originally posted by LURCH
That seems equitable. C'mon, Chroot, let's hear from ya!

He teaches. It is summer time. Teachers do not work in the summer.

 

[marcus]

Originally posted by Labguy
He teaches. It is summer time. Teachers do not work in the summer.

Well SOMEBODY go!

 

[Labguy]

Originally posted by marcus
Well SOMEBODY go!

Ok, I have been away for a long time on "sick-leave". This might have been asked before, but I'm not going to read 20(x) pages to find out.

Question:
When and where (who is a bonus) were the first redshifts measured (taken?) indicating that the Andromeda galaxy was moving with respect to us?

 

[LURCH]

My power's been out the last two days (maybe you heard about it?).

Thanks for covering for me, Labguy.